The present invention, in some embodiments thereof, relates to navigation systems and, more specifically, but not exclusively, to locating devices interfering with navigation satellite signals.
A Satellite Navigation System (SNS) receiver determines its position by extracting its distance to navigation satellites. The satellite navigation system may have coverage for worldwide (global), regional, national, and the like, geographic areas. For example, the NAVSTAR Global Positioning System (GPS), the Russian GLObal NAvigation Satellite System (GLONASS), the European Union's Galileo positioning system, and the like, are Global Navigation Satellite System (GNSSs). For example, China's BeiDou Navigation Satellite System is a regional SNS.
Given the satellite's location and given the exact distance from each satellite to the SNS receiver, the SNS receiver's location may be computed using triangulation functions. Since those distances are computed by Time-Of-Arrival (TOA) methods, inherent errors are inevitable, such as satellite signal delays caused by the atmosphere, and the like. Contemporary commercial SNS receivers may reach an error between 2 to 5 meters in open sky locations, and in dense urban regions, the error may be as high as 50 meters or more.
Most commercial navigation applications handle such errors, while military and security SNS dependent systems need higher location accuracy. For some systems, knowing the location error is important, such as in risk awareness, evaluation of SNS dependent systems, such as marine or air traffic control systems, and the like. Estimating the SNS receiver's location error may be used for improving the SNS receiver's location accuracy.
Modern commercial SNS receivers are accurate in standard open regions, therefore uncertainty in the reported location may be caused by malfunction, such as a broken antenna, external interference, and/or the like. External SNS signal interference may be accidental interference, such as electromagnetic radiation noise, lack of satellite visibility due to obstructions, and/or the like, or deliberate interference, such as SNS Jamming, Spoofing, and/or the like. Estimating the location error may be relevant in both internal and external interferences.
SNS jammers are devices that generate electromagnetic radiation noise in the carrier frequency of the SNS, such as 1.57 GHz for the L1 global positioning system (GPS), and the like. A SNS jammer transmits electromagnetic radiation noise received by the SNS receiver, thereby degrading the Signal to Noise Ratio (SNR), such as when the SNS receiver is unable to report its location, referred to as loosing SNS fix. Jamming behavior is characterized by a sharp degradation of the satellites signal SNR values. Different SNS jammers produce different ranges from several meters to several kilometers.
While jamming mainly causes signal noise at the SNS receiver, a more sophisticated jamming method exists for deliberate interference of SNS signals, known as spoofing. SNS spoofers are transmitters that emit signals identical to those sent by the SNS satellites to attempt to mislead the SNS receiver. During a spoofing attack, the SNS receiver loses its satellite lock on the genuine satellites.
SNS jamming interference is a major concern both in civilian and military industries. SNS jamming affects not only SNS receivers, but also SNS dependent systems, such as air traffic control systems, and the like.